Modelling the effects of biological traits on maternal beef cow efficiency

Abstract

A model of maternal biological factors was developed to investigate the effects that they would have on the biological efficiency of a beef cow herd on NZ Class 2 Hill Country. In the model there was four different treatments imposed, mature cow weight at weaning, sire weight, lactation potential and pasture supply and quality. The three different mature cow weights used were 400kg, 500kg and 600kg. Sire weight was similar being 450kg, 500kg and 650 kg. Lactation potential was modelled at three different levels, low, medium and high. Total yield for the length of the lactation was subsequently 1534kg, 1753kg and 1973kg for each lactation treatment. Pasture supply modelled was developed and undeveloped hill country from a South Canterbury field trial. From this the feed profiling model could work out the output and inputs for each scenario in terms of energy required and kg of calf produced at weaning. This allowed the effect that each factor had on the maternal efficiency to be quantified. Lactation potential has the biggest effect on calf weights to weaning, with calves on cows with high lactation potential being on average, 18.4kg heavier at weaning than those on medium lactation potential. In regards to efficiency, kg calf weaned per kg of cow at weaning, lactation potential and mature cow weight of the cow had the biggest effect, with cows that had a low mature weight and high lactation potential being the most efficient (56-60%). Cows with a high mature weight and low lactation potential had the worst efficiency at 32-33%. To improve the efficiency of the beef cow herd in NZ it would be to crossbreed and fuse high lactation potential genetics into beef cow herds, whilst focusing on a smaller more productive cow. This will allow heavier weights at weaning, and through this model has demonstrated that these cows are the most efficient convertors of grass to kg of gain in calf weights to weaning.